1. Field of the Invention
The present invention relates generally to a light modulator package and, more particularly, to a light modulator package having an inclined light transmissive lid which is manufactured or positioned such that a surface of the light transmissive lid is inclined relative to a reflective surface of a light modulating array.
2. Description of the Related Art
As the Internet and mobile phones have become popular, the information age is rapidly arriving, and the amount of information is dramatically increasing. Further, the construction of infrastructure for information systems is becoming a matter of primary concern of a national undertaking.
This inevitably requires the communication and storage of information. The affordability, miniaturization, high-capacity, and digitization of information and communication devices, information displays, and recording devices have been achieved. Faster data transmission and storage of a greater amount of data in a limited space are required. Further, the market demand for products increasing a user's convenience and mobility is continuously growing.
Meanwhile, a micromachining technology has been developed, which manufactures micro-optical parts including a micromirror, a micro lens, and a switch, a micro inertia sensor, a micro biochip, and a micro wireless communication device, using a semiconductor device manufacturing process.
Further, MEMS designating the micromachining technology, devices and systems manufactured by the micromachining technology have been established as an independent manufacturing technology and application field.
The MEMS are called micro-electro-mechanical systems or devices, and are applied to an optical field. When using the micromachining technology, it is possible to manufacture an optical part smaller than 1 mm. Thereby, a micro-optical system can be attained. A separately manufactured semiconductor laser is mounted on a holder which is manufactured through the micromachining technology, and a micro Fresnel lens, a beam splitter, and a 45° reflecting mirror are manufactured through the micromachining technology and subsequently assembled. A conventional optical system is configured such that the mirror, the lens, etc. are mounted on a large and heavy optical bench using an assembling tool. The laser is also large in size. In order to obtain desired performance of the optical system configured as described above, a precise stage and much effort are required to arrange an optical axis, a reflecting angle, a reflective surface, etc.
However, the micro optical system is advantageous in that it reduces the tools, space, and effort required, in addition to achieving performance different from that of the conventional optical system.
The micro optical system has several advantages, that is, fast response speed, reduced light loss, and easy integration and digitization. Due to such advantages, the micro optical system is adapted and applied to information and communication devices, information displays, and recording devices.
Conventionally, an accelerometer, a pressure sensor, an inkjet head, a head for hard discs, a projection display, a scanner, micro fluidics, and others are produced using the MEMS technology and are commercialized. Recently, due to the development of optical communication technology, interest in technology realizing higher performance optical communication parts is increasing.
Particularly, people have an increasing interest in a spatial light modulator using a switching technique which drives the micromirror by an actuator in the MEMS manner. Such a light modulator is advantageous in that it has high speed, parallel processing capacity, and mass information processing capability, unlike the conventional digital information processing technology which is problematic in that it is impossible to process a great amount of data in real time.
At present, studies have been conducted on the design and production of a binary phase only filter, an optical logic gate, a light amplifier, image processing technique, an optical device, a light modulator, etc. using the above-mentioned light modulator. Especially, the spatial light modulator is adapted to optical memory, optical display devices, printers, optical connections, holograms, and displays.
The light modulator is embodied by a reflective deformable grating light modulator 110 as shown in FIG. 1. The light modulator 110 is disclosed in U.S. Pat. No. 5,311,360 by Bloom et al. The modulator 110 includes a plurality of reflective deformable ribbons 118, which have reflective surface parts, are suspended on an upper part of a silicon substrate 116, and are spaced apart from each other at regular intervals. An insulating layer 111 is deposited on the silicon substrate 116. Subsequently, a sacrificial silicon dioxide film 112 and a silicon nitride film 114 are deposited.
The nitride film 114 is patterned by the ribbons 118, and a portion of the silicon dioxide film 112 is etched, thereby maintaining the ribbons 118 on the oxide spacer layer 112 by a nitride frame 120.
In order to modulate light having a single wavelength of λo, the modulator is designed so that the thickness difference between the ribbon 118 and an oxide spacer 112 is equal to λo/4.
Limited by a vertical distance d between a reflective surface 122 of each ribbon 118 and a reflective surface of the substrate 116, a grating amplitude of the modulator 110 is controlled by applying voltage between the ribbon 118 (the reflective surface 122 of the ribbon 118 acting as a first electrode) and the substrate 116 (a conductive layer 124 formed on a lower side of the substrate 116 to act as a second electrode).
However, the light modulator of Bloom uses an electrostatic manner to control the position of the micromirror. In this case, the light modulator is problematic in that an operating voltage is relatively high (about 20V or so), and the relation between applied voltage and displacement is nonlinear. Consequently, such a light modulator cannot reliably control light.
The MEMS elements as well as the reflected light modulator of Bloom have ultra-fine actuators so that the MEMS elements are greatly sensitive to the external environment, including temperature, humidity, micro-dust, vibration and impact, and thereby a proper method of sealing is required.
U.S. Pat. No. 6,303,986 discloses a method and apparatus for sealing MEMS elements using a hermetic lid to provide an MEMS package.
Herein below, the construction of the MEMS package disclosed in U.S. Pat. No. 6,303,986, in which the lid glass hermetically seals the MEMS elements from the external environment, will be described with reference to FIG. 2.
FIG. 2 shows a representative sectional view of the MEMS package in which the transparent lid hermetically seals the MEMS element. As shown in FIG. 2, a conductive ribbon 300 having a metallic conductive/reflective covering 302 is formed over an upper surface of a semiconductor substrate 304, with an air gap 306 defined between the ribbon 300 and the substrate 304.
A conductive electrode 308 is formed on the upper surface of the substrate 304 and covered with an insulation layer 310. The conductive electrode 308 is placed under the ribbon 300 at a position under the air gap 306.
The conductive/reflective covering 302 extends beyond the region of the mechanically active ribbon 300 and is configured as a bond pad 312 at its distal end. The MEMS package is also passivated with a conventional overlying insulating passivation layer 314 which does not cover the bond pads 312 or the ribbon structures 300 and 302.
Control and power signals are coupled to the MEMS package using conventional wire-bonding structures 316.
Unlike conventional semiconductor manufacturing techniques in which semiconductor elements are packed densely onto the upper surface of a semiconductor substrate, an optical glass is hermetically sealed directly onto the semiconductor substrate in the above-mentioned U.S. patent. Thus, the bond pads 312 are spaced a considerable distance from the ribbon structures 300 and 302, so that a lid sealing region 318 is provided. A solderable material 320 is formed onto the lid sealing region 318.
The hermetic lid 322, which is joined to the semiconductor substrate, is preferably formed of an optical quality material. Thus, the lid 322 can be used for a variety of purposes including filtering undesired radiation, enhancing reflectivity, or decreasing reflectivity.
The lid 322 may be also coated with an optically sensitive material to be used for other purposes without being limited to the above-mentioned purposes.
Once the lid 322 is formed to a size appropriate to fit concurrently over the lid sealing region 318, with a solderable material 324 formed in a ring surrounding the periphery of one surface of the lid 322, solder 326 is deposited onto the solderable material 324 so that the lid 322 is joined to the semiconductor substrate.
Though not shown to scale in the drawing, a significant space exists between the lid 322 and the ribbon structures 300 and 302 to prevent them from interfering with one another. Thus, the ribbon structures 300 and 302 are free to move upwards and downwards.
FIG. 3 shows a plan view of an exemplary package disclosed in the above-mentioned US patent wherein various regions are shown as blocks. As shown in the drawing, the ribbon structures of a GLV (diffraction grating light valve) to be used as a display engine comprise a mechanically active region 340, while the lid sealing region 318 surrounds the mechanically active region 340.
In this case, the lid sealing region 318 is passivated and includes no mechanically active elements, such as those traditionally found in MEMS devices.
Furthermore, the lid sealing region 318 includes no bond pads where other off-chip interface structures, such as the lid 322, would interfere with the effective operation of the MEMS device. However, it is possible that the lid sealing region 318 could include active electronic elements. In the event that the lid sealing region 318 did include active electronic elements, effort must be taken to planarize that region in order to provide the surface to which the lid 122 can properly mate.
The bonding region 342 surrounds the lid sealing region 318, and includes several bond pads necessary for making interconnection from the package to off-chip circuits and systems.
As described above, the lid is usually positioned parallel to the reflective surface of the light modulator. Thus, due to the scattering over the reflective surface of the light modulator, undesired optical noise is generated, and thereby the optical noise deteriorates the performance of the light modulator.
FIG. 4 is a view to illustrate the optical noise of a conventional light modulator package. In the drawing, reference numeral 500 denotes a substrate, reference numeral 510 denotes a light modulating element, and reference numeral 532 denotes a light transmissive lid.
Referring to the drawing, the conventional light modulator package generates three types of optical noise.
(1) SLS (Surrounding Landscape Scattering) is the optical noise caused by reflection and scattering in an optical system.
(2) WR (Window Reflections) is the optical noise caused by the reflection on the light transmissive lid (especially, the light transmissive window), and comprises first WR (FWR) and second WR (Second WR). The FWR is the optical noise caused by the reflection of light incident through the light transmissive window of the light transmissive lid 532, while the SWR is the optical noise caused by the reflection of light diffracted on the light modulating element 510. As shown in the drawing, the FWR includes reflected light 1-1, 1-2, and 1-3. In this case, incident light 1 is reflected on a surface of the light transmissive lid 532, thus generating the reflected light 1-1. The incident light 1 passes through the light transmissive lid 532, and thereafter is reflected on an inner surface of the lid 532, thus generating the reflected light 1-2. Further, the light reflected on the inner surface of the light transmissive lid 532 is reflected on an outer surface of the lid 532 and reflected on the inner surface of the lid 532 again, thus generating the reflected light 1-3. Meanwhile, the SWR includes reflected light 2-1 and 2-2. Diffracted light 2 is generated by the light modulating element 510. The diffracted light 2 is reflected on the outer surface of the light transmissive lid 532 and reflected on the inner surface of the lid 532 again, thus generating the reflected light 2-1. The reflected light 2-1 is reflected on the outer surface of the lid 532 and reflected on the inner surface of the lid 532 again, thus generating the reflected light 2-2.
(3) GBR (Gap Bottom Reflection) is the optical noise caused by the reflection and scattering from a lower surface of the light modulating element 510. Although not shown in the drawing, incident light passing through a gap between one light modulating element and a neighboring light modulating element is reflected on the substrate 500, thus causing optical noise. This optical noise is called GBR.
Such optical noise negatively affects light devices, such as the optical modulator. Especially, in the event that the light transmissive lid approaches the light modulating element so as to miniaturize the light modulator package, the effect of the optical noise is serious. Therefore, the optical noise must be eliminated so as to accomplish the miniaturization of the light modulator package.